火星沉降H-ENA的分布与特性

张艺腾; 李磊; 谢良海; 苟晓晨; 冯永勇

doi:10.11728/cjss2024.02.2023-0044

火星沉降H-ENA的分布与特性

doi: 10.11728/cjss2024.02.2023-0044 cstr: 32142.14.cjss2024.02.2023-0044

张艺腾^{1, 2, 3, 4,},
李磊^{1, 3, 4,},
谢良海^{1, 3, 4},
苟晓晨^{1, 3, 4},
冯永勇^{1, 3, 4}

1.
中国科学院国家空间科学中心空间天气学国家重点实验室　北京　100190
2.
中国科学院大学　北京　100049
3.
中国科学院国家空间科学中心　北京　100190
4.
中科–莘县联合研究中心　聊城　252400

基金项目: 国家自然科学基金项目(42241112, 42122032), 中国科学院重点部署项目(ZDBS-SSW-TLC00103), 民用航天预先研究项目(D020104), 国家重点实验室专项研究基金和中国科学院国家空间科学中心“攀登计划”项目共同资助

详细信息

作者简介:

张艺腾：男, 1981年11月出生于辽宁省沈阳市. 现为中国科学院国家空间科学中心副研究员, 硕士生导师. 主要研究方向为火星空间环境、高精度磁场探测与应用等. E-mail: ytzhang@nssc.ac.cn

李磊：女, 中国科学院国家空间科学中心研究员. 主要从事行星空间环境探测研究. E-mail: lil@nssc.ac.cn

中图分类号: P353
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出版历程
- 收稿日期: 2023-04-07
- 修回日期: 2023-04-20
- 网络出版日期: 2023-12-15

Distribution and Characteristics of Martian Precipitating H-ENA

ZHANG Yiteng^{1, 2, 3, 4
,},
LI Lei^{1, 3, 4
,},
XIE Lianghai^{1, 3, 4},
GOU Xiaochen^{1, 3, 4},
FENG Yongyong^{1, 3, 4}

1.
State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing 100190
2.
University of Chinese Academy of Sciences, Beijing 100049
3.
National Space Science Center, Chinese Academy of Sciences, Beijing 100190
4.
Joint Research and Development Center of Chinese Science Academy and Shen County, Liaocheng 252400

摘要

摘要: 能量中性原子(Energetic Neutral Atom, ENA)是由能量离子与中性背景成分电荷交换产生. 火星的外逸层扩展范围远高于弓激波, 上游太阳风质子与其相互作用并转化为太阳风氢ENA(Hydrogen-ENA, H-ENA), 新生的H-ENA可直接进入低层大气, 成为新的物质与能量输运通道. 本文基于单流体多成分MHD模型与中性外逸层模型, 计算了火星200 km等高面沉降H-ENA通量的空间分布, 统计了多种太阳风条件下沉降H-ENA的粒子与能量沉降率, 分析影响因素. 结果表明, 在一定模拟条件下, 产生于弓激波上游的太阳风H-ENA, 呈cosZ分布(Z为天顶角), 受磁异常影响较小, 是沉降H-ENA的主要成分, 占ENA总沉降量的59%, 占能量沉降的81%; 产生于磁鞘的磁鞘H-ENA受磁异常阻碍影响较大, 在最强磁异常上方其沉降通量显著下降; 沉降H-ENA与上游太阳风的通量呈正比例关系; 2.1%～3.5%上游太阳风质子转化为太阳风H-ENA.
- 火星 /
- 沉降H-ENA /
- MHD模型 /
- 磁异常
Abstract: Energetic Neutral Atom (ENA) is generated by charge exchange between energetic ions and background neutrals. As Martian exosphere extends far above the bow shock, hydrogen ENA (H-ENA) produced by solar wind proton may enter the lower atmosphere directly, depositing mass and energy in the atmosphere. Based on the single-fluid multispecies MHD model and exosphere model, this paper calculates the spatial distribution of the precipitating H-ENA flux at the height of 200 km on Mars, evaluates the particle and energy deposition rate of the precipitating H-ENA under different solar wind conditions, analyzes their controlling factors. The results show that the solar wind H-ENA generated upstream of the bow shock is less affected by the crustal fields, and shows a cosZ distribution. As a major mass and energy source, the precipitating solar wind H-ENAs account for 59% particle deposition and 81% energy deposition of the total precipitating ENAs. Magnetosheath H-ENA generated in the magnetosheath is greatly affected by the crustal fields, and their precipitating flux decreases significantly above the strongest magnetic anomalies. The precipitating H-ENA flux is proportional to the upstream solar wind flux, and 2.1%～3.5% of upstream solar wind protons are estimated to be converted into the solar wind H-ENAs.
- Mars /
- Precipitating H-ENA /
- MHD model /
- Crustal

HTML全文

图 1 MHD模型的仿真结果. 在MSO (Mars Solar Orbital) 坐标系xz平面内各物理量的空间分布

Figure 1. Simulation result of MHD model. Spatial distribution of physical quantities on the xz plane in the MSO (Mars Solar Orbital) frame

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图 2 质子与 H原子、H₂分子、O原子的电荷交换截面曲线

Figure 2. Cross-section of charge exchange between proton and atomic H, H₂ and atomic O

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图 3 H-ENA产生率的全球分布

Figure 3. Global distribution of H-ENA production rate

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图 4 200 km等高面上沉降太阳风H-ENA通量的空间分布. (a)沉降太阳风H-ENA通量的经纬度分布, (0, 0)表示日下点. (b)沉降太阳风H-ENA通量随太阳天顶角(Z)的变化

Figure 4. Spatial distribution of solar wind H-ENA flux at 200 km. (a) Longitude and latitude distribution of the precipitating solar wind H-ENA flux, and (0, 0) represents the subsolar point. (b) Variation of the precipitating solar wind H-ENA flux with the solar zenith angle (Z)

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图 5 200 km等高面上沉降磁鞘H-ENA通量的空间分布

Figure 5. Spatial distribution of precipitating magnetosheath H-ENA flux at 200 km

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图 6 200 km等高面上沉降H-ENA通量随太阳天顶角Z的变化(方向角为该位置与日下点连接弧线相对于日下点地理北向的方向角)

Figure 6. Variation of precipitating H-ENA flux on 200 km constant elevation surface with solar zenith angle Z (Direction angle is from the connection arc between the precipitating position and subsolar point to the geography north of the subsolar point)

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图 7 太阳风通量与沉降H-ENA通量以及沉降率的关系

Figure 7. Relation between solar wind flux and the precipitating H-ENA flux, particle deposition rate

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图 8 模拟H-ENA定向微分通量图像. 模拟观测位置为MSO坐标系下(–1.5, 2.6, 0), 视场为指向火星的半空间2π视场

Figure 8. Image of simulated H-ENA directional differential flux. Virtual observation position is (–1.5, 2.6, 0) in MSO frame, the field of view is 2π in half space field facing to Mars

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表 1 MHD模型的参数

Table 1. Parameters of MHD model

太阳风参数	值
密度/cm^–3	1.8
速度/(km·s^–1)	(500, 0, 0)
质子温度/K	1.5×10⁵
磁场/nT	(–1.6, 2.5, 0)

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表 2 临界高度170 km处外逸层模型参数

Table 2. Model parameters at exospheric critical altitude 170 km

成分	温度/K	密度/cm^–3
H	192	9.9×10⁵
H₂	192	3.8×10⁶
O(thermal)	173	1.4×10⁸
O(hot)	4.4×10³	5.5×10³

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表 3 不同磁异常条件下沉降H-ENA物理量统计

Table 3. Statistics on precipitating H-ENA parameters under different crustal field conditions

模型条件 (最强磁异常)	沉降太阳风 H-ENA			沉降磁鞘 H-ENA
模型条件 (最强磁异常)	最大通量(×10¹⁰)/(m^–2·s^–1)	沉降率 (×10²⁴)/ s^–1	能量沉降率(×10²⁷)/(eV·s^–1)	最大通量(×10¹⁰)/(m^–2·s^–1)	沉降率 (×10²⁴)/ s^–1	能量沉降率 (×10²⁷) /(eV·s^–1)
Case 1 无	2.11	0.84	1.06	1.89	0.83	0.57
Case 2 位于子夜	2.06	0.80	1.01	1.59	0.70	0.47
Case 3 位于正午	1.87	0.72	0.91	1.33	0.50	0.21

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表 4 不同太阳风条件下沉降H-ENA物理量统计

Table 4. Statistics on precipitating H-ENA parameters under different solar wind conditions

模型说明	太阳风	沉降太阳风 H-ENA		沉降磁鞘 H-ENA
模型说明	通量 (×10¹²)/( m^–2·s^–1)	最大通量 (×10¹⁰ )/(m^–2·s^–1)	沉降率 (×10²⁴)/ s^–1	最大通量 (×10¹⁰)/(m^–2·s^–1)	沉降率 (×10²⁴)/s^–1
表3中Case 3	0.90	1.87	0.72	1.33	0.50
CME到达前	2.71	9.03	3.59	6.93	2.47
CME到达后	10.94	38.36	14.96	28.80	11.60

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